Traditional photofinishing operations for photographic color images provide the consumer with a variety of textures to the surface of the image in addition to the usual glossy print. In traditional silver halide photography the texture is applied to the surface of the receiving paper in its manufacturing process and survives liquid processing and drying in the photofinishing operation.
In electrophotography, multicolor images having resolution and other qualities comparable to those of silver halide photography have been produced in the laboratory. One reason such systems have not been commercially pratical is they have generally required liquid developing for high quality. However, recent advances in fine particle dry toners have made low grain, high resolution images feasible with dry systems.
One of the problems associated with such systems is that of providing the customer a variety of textures to the image comparable to that available with ordinary photofinishing. Highest quality dry color imaging is accomplished with a receiving sheet having a thermoplastic layer which can be texturized. However, the fixing and other treatments associated with dry electrophotography involve the application of heat and pressure which would adversely affect any texture imparted to such a receiving sheet in its manufacturing operation.
U.S. Pat. No. 4,639,405 shows a post-treatment step to add gloss to a toner image carried on paper after ordinary fusing. The fixed image-bearing paper is dried and then pressed between a pair of heated rollers which increase the gloss of the image. At least one of the rollers has a resin coating to provide some width of nip to aid in heat transfer. A purpose for the drying step is to prevent blistering from steam escaping around the nip when coated paper is used as the receiving sheet.
U.S. Pat. No. 4,780,742 shows a method of increasing the gloss of a fixed toner image by coating it with a thin sheet in the presence of heat and pressure. The thin sheet packs the image and fuses it together, increasing gloss and removing surface roughness. The sheet is cooled and peeled off. The image appears to be fused on top of the support and has a principle object of providing less scattering for color images on transparencies.
European patent application No. 0 301 585 published Feb. 1, 1989, shows a glazing sheet used to increase the gloss of either a toner image on a paper backing or a dye and developer in a thermoplastic coating. The glazing sheet is pressed against the paper sheets with moderate pressure and the dye-thermoplastic sheets with substantial pressure. The glazing sheet can be either smooth for a high gloss or dull for a low gloss finish. In one embodiment, the glazing sheet has both high and low gloss sections that can be selected.
In the latter two references the image and sheet are allowed to cool before separation. This approach to preventing release in pressure fixing is shown in a large number of references; see, for example, European patent application No. 0 295 901 and U.S. Pat. No. 3,948,215.
U.S. Pat. No. 4,337,303 suggests a method of thermal transfer involving bringing a receiving sheet having a thermoplastic coating into contact with fine toner images in the presence of sufficient heat to soften the thermoplastic coating. The toner is said to be "encapsulated" by the thermoplastic coating under moderate pressure.